Glass Yarn for Reinforcing Organic and/or Inorganic Materials

ABSTRACT

The invention relates to glass reinforcement strands, the composition of which comprises the following constituents in the limits defined below, expressed as percentages by weight: 59 to 63% SiO 2 ; 10 to 16% Al 2 O 3 ; 16 to 23% CaO; 1 to 3.2% MgO; 0 to 2% Na 2 O+K 2 O+Li 2 O; 0 to 1% TiO 2 ; 0.1 to 1.8% B 2 O 3 ; 0 to 0.5% Li 2 O; 0 to 0.4% ZnO; 0 to 1% MnO; and 0 to 0.5% F. These strands have improved properties in terms of mechanical strength, acid resistance and high-temperature resistance for a low-cost composition. The invention also relates to a process for producing the said strands and to the composition allowing them to be produced.

The present invention relates to glass strands or fibres, especiallythose intended for reinforcing organic and/or inorganic materials andable to be used as textile strands, these strands being able to beproduced by a process consisting in mechanically attenuating streams ofmolten glass emanating from orifices placed at the base of a bushing,generally heated by resistance heating.

The invention relates more particularly to glass strands having aparticularly advantageous novel composition.

The field of glass reinforcement strands is one particular field of theglass industry. These strands are produced from specific glasscompositions, the glass used having to be able to be attenuated into theform of filaments a few microns in diameter, using the process describedabove, and having to allow the formation of strands capable inparticular of fulfilling their reinforcement role. The glassreinforcement strands most commonly used are thus strands formed fromglasses whose composition derives from the eutectic composition of theSiO₂—Al₂O₃—CaO ternary diagram, the liquidus temperature of which is1170° C. These strands are referred to by the name of “E-glass” strands,the archetype of which is described in the patent publications U.S. Pat.No. 2,334,981 and U.S. Pat. No. 2,571,074, which strands have acomposition essentially based on silica, alumina, lime and boricanhydride. The latter compound, present with contents ranging inpractice from 5 to 13% in glass compositions for “E-glass”, is added asa replacement for silica so as to reduce the liquidus temperature of theglass formed and to make it easier for the glass to melt. The term“liquidus temperature”, denoted by T_(liq), is the temperature at which,in a system in thermodynamic equilibrium, the most refractory crystalappears. The liquidus temperature therefore gives the lower limit atwhich it is possible to fiberize the glass.

E-glass strands are furthermore characterized by a limited content ofalkali metal oxides (essentially Na₂O and/or K₂ 0).

Since the two abovementioned patent applications, glasses comprisingthese constituents have undergone numerous modifications with thepurpose of reducing emanations of products liable to pollute theatmosphere, of reducing the cost of the composition by decreasing thecontent of the most expensive constituents, of improving the capabilityof these glasses to undergo fiberizing (fiberizing or formingcorresponding to the operation of attenuating the glass filaments comingfrom a bushing using the process described above), especially byreducing their viscosity at high temperatures and their tendency todevitrify, or finally of improving one particular property intended toincrease their performance (or to make them suitable) for certainapplications.

Solutions for greatly reducing polluting emanations have consisted ineliminating the most volatile elements from the compositions, thesebeing boric anhydride and fluorine. Decreasing the boric anhydridecontent is also a means of reducing the cost of the compositions. Theelimination of boric anhydride and fluorine in the compositions of theseglasses is generally to the detriment of their fiberizability and theirprocessing in order to obtain reinforcement strands, which generallybecomes more difficult or tricky, possibly requiring modifications toexisting fiberizing installations.

The publication U.S. Pat. No. 3,847,626 describes and claimscompositions in which these elements have been replaced with highcontents of titanium oxide, ranging from 3 to 5%, and with magnesia,contents ranging from 1.5 to 4%. These two oxides make it possible tocompensate for the absence of boron and fluorine, making the glassesformed from these compositions suitable for fiberizing. However, theyellow coloration conferred by such levels of titanium tends to excludethis type of composition for certain applications. High titanium oxidecontents, ranging from 2 to 4%, are also recommended in Publication U.S.Pat. No. 4,026,715, this constituent generally being added together withdivalent oxides such as SrO, ZnO or BaO, which furthermore have thedisadvantage of being expensive.

Publication U.S. Pat. No. 4,199,364 describes compositions having highlithium oxide contents. Apart from its high cost, lithium oxide formspart of the alkali metal oxides, which are known to degrade thecapability of the fibres to reinforce electronic circuit substrates.

Application WO 96/39362 describes compositions containing neither boronnor fluorine, which are essentially formed from the SiO₂—Al₂O₃—CaO—MgOquaternary system, containing small amounts of titanium oxide (less than0.9%) and generally containing no additions of expensive oxides such asthose described in the aforementioned applications. However, theseglasses have a liquidus temperature and a forming temperature that arerelatively high.

In the field of glass strands obtained by mechanical attenuation ofmolten glass streams, the term “forming temperature” is the temperaturefor which the glass possesses a viscosity of 1000 poise(decipascals.second), around which viscosity the glass must befiberized. This temperature, denoted T_(log 3), corresponds moreparticularly to the temperature of the glass at the bushing nipples. Thetemperature of the glass on entering the bushing corresponds to aviscosity of the order of 10^(2.5) poise, and is denoted by T_(log 2.5).

To avoid any risk of devitrification during forming, the “fiberizingrange”, denoted by ΔT and defined as the difference between the formingtemperature and the liquidus temperature, must be positive andpreferably greater than 50° C.

High values of these various temperatures require the glass to bemaintained at high temperatures both during the conditioning of theglass and in the fiberizing device itself.

This drawback results in an additional cost due to the additional supplyof heat needed to condition the glass and to more frequent renewal ofthe fiberizing tools, especially the parts made of platinum, the ageingof which is greatly accelerated by the increase in temperature.

More recently, several applications have also disclosed compositions forobtaining low-cost glasses, which possess liquidus and formingtemperatures close to those of E-glass, therefore allowing them to befiberized more easily.

Thus, Patent Publications WO 99/12858 and WO 99/01393 describe glasscompositions containing small amounts of fluorine or boron oxide. In WO00/73232, the lowering of the characteriztic temperatures is achieved bycompositions having a low MgO content (less than 1% ) and by theaddition of a certain amount of boron oxide or lithium oxide or zincoxide or even manganese oxide, thereby lessening the economic advantageof these compositions. WO 00/73231 discloses compositions whose liquidustemperature is lowered, especially thanks to the addition of MgO withina narrow range of contents, between 1.7 and 2.6%. Most of thecompositions exemplified in the above application furthermore include anoxide chosen from boron oxide, lithium oxide, zinc oxide or evenmanganese oxide. The reduction in characteriztic temperatures of theprocess can also be achieved, in WO 01/32576, by the low silica contents(less than 58% ) of the compositions, and in WO 02/20419, by selectingcompositions whose silica content/alkaline-earth metal content ratio isless than 2.35.

The objectives pursued by the various inventions mentioned were mainlyto reduce the cost of the compositions and to reduce the amount ofenvironmentally harmful materials discharged. The use of fibres forcertain applications has also dictated the choice of very specificcompositions. Thus, three properties may be particularly sought after:acid resistance, resistance at high temperatures and high mechanicalstrength, especially tensile strength, of the fibres. The first propertyis particularly desired in applications of reinforcing organic and/orinorganic materials which come into contact with an acid medium, forexample in the chemical industry. The second property is of paramountimportance when the glass strands are used for example in exhaustsystems for motor vehicles. The third property is sought when thematerials reinforced by the glass strands are subjected to highmechanical stresses.

For each of these properties, particular compositions have beendeveloped.

Publications WO 03/050049 and WO 02/42233 describe glass fibres suchthat their composition makes them suitable for being employed in motorvehicle exhaust systems. In the first application, the objective isachieved thanks to a glass composition containing very small amounts(less than 1% ) of MgO. These glasses also contain high contents (atleast 1.5% ) of titanium oxide. The second application describes glasscompositions containing a particular range of alkaline-earth metal oxidecontents. Many examples in this application are glasses that containbarium oxide or strontium oxide. Document FR-A-2 804 107 describesfibres having a particular composition, the high-temperature resistanceproperty of which stems from a treatment of their surface for thepurpose of obtaining an extremely silica-enriched surface composition.

Application FR-A-2 692 248 describes and claims glass compositions whichbehave, during melting and during fiberizing, in a manner similar toE-glass, but which possess a markedly superior acid resistance,especially thanks to the reduction in boric anhydride and aluminacontents. Nevertheless, the glasses claimed do possess a boric anhydridecontent of even greater than 2%.

The above examples show that specific compositions have been developedin order to meet certain technical, economic or environmentalconstraints but that the optimization of a single range of compositions,allowing all of these constraints to be met, which from the industrialstandpoint is highly desirable, remains to be accomplished.

One object of the present invention is therefore to propose glasscompositions of advantageously low cost which exhibit good formabilityand make it possible to obtain glass strands having high-temperatureresistance, acid resistance and mechanical strength properties that aresignificantly improved over those of E-glass and/or are similar tocertain currently available glasses while exhibiting better formability.

Another object of the invention is to propose glass compositions which,when they are being melted, give off little emanation liable to damagethe environment.

These objects are achieved thanks to glass strands whose compositioncomprises the following constituents in the limits defined below,expressed as percentages by weight:

SiO₂ 59 to 63 Al₂O₃ 10 to 16 CaO 16 to 23 MgO 1 to less than 3.2 Na₂O +K₂O + Li₂O 0 to 2 TiO₂ 0 to 1 B₂O₃ 0.1 to 1.8 Li₂O 0 to 0.5 ZnO 0 to 1MnO 0 to 1 F 0 to 0.5.

Silica is an oxide acting as a glass network former, and plays anessential role in stabilizing the glass. Within the limits definedabove, when the percentage of this constituent is less than 58%, theglass obtained is not viscous enough and it devitrifies too easilyduring fiberizing. For contents above 63%, the glass becomes veryviscous and difficult to melt. Consequently, the silica content ispreferably less than 62.5% and particularly preferably less than 62%.Since silica plays an essential beneficial role in acid corrosionresistance, its content is preferably greater than 60%, especially 60.5%or greater, and even 61%. A particularly preferred compromise consistsin choosing a silica content of between 60 and 61%.

Alumina also constitutes a network former in the glasses according tothe invention and plays a fundamental role in their stability. Withinthe limits defined according to the invention, a content of less than10% causes a substantial increase in the hydrolytic attack of the glass,whereas increasing the content of this oxide to above 16% runs the riskof devitrification and an increase in the viscosity. Owning to itsdeleterious effect on the acid corrosion properties, the alumina contentis preferably maintained below 15% or even 14%. The greatest resistanceto devitrification is obtained for alumina contents of between 11 and14%, preferably between 12 and 13%.

Lime and magnesia make it possible to adjust the viscosity and controlthe devitrification of the glasses according to the invention. Withinthe limits defined according to the invention, a CaO content of 23% orhigher results in an increase in the rates of devitrification to CaSiO₃(wollastonite) prejudicial to good fiberizing. The CaO content musttherefore be maintained at a value strictly less than 23%. A CaO contentof less than 16% results in too low a hydrolytic resistance. The CaOcontent is therefore preferably greater than 18%, and even greater than20%. The MgO content, together with the lime content, makes it possibleto obtain glasses of which the liquidus temperature is particularly low.This is because the addition of magnesia in defined contents makes itpossible to introduce a competition between the growth of wollastoniteand diopside (CaMgSi₂O₆) crystals, this having the effect of reducingthe rate of growth of these two crystals, and therefore of giving gooddevitrification resistance. The MgO content is greater than 1%. The MgOcontent is also preferably maintained at 3% or lower, but greater than2%, and especially 2.2% or higher, or indeed 2.6. For contents of 3.2%or higher, the rate of crystallization of diopside is too great. Forthis reason, the MgO content of the glasses according to the inventionis strictly less than 3.2%.

The alkali metal oxides may be introduced into the compositions of theglass strands according to the invention in order to limitdevitrification and reduce the viscosity of the glass. However, thealkali metal oxide content must be less than 2% in order to avoid anunacceptable increase in the electrical conductivity for applications inthe electronics field and to avoid a detrimental reduction in thehydrolytic resistance of the glass. The lithium content must especiallybe maintained below 0.5% and preferably below 0.1%. The inventors havedemonstrated the extremely deleterious role of alkali metal oxides inthe high-temperature resistance, especially characterized by theirsoftening temperature. This role is known in general, but within thisparticular context the effect on the reduction in characteristictemperatures at which the glass softens, due to very low alkali metaloxide contents has turned out to be astonishingly great. The totalcontent of alkali metal oxides therefore preferably does not exceed1.5%, or even 1%.

TiO₂ plays an important role in the glasses according to the invention.This oxide is known as a flow promoter for the glass and is capable ofreducing the liquidus temperature, and thereby partially replacing boronoxide. Beyond 1%, the yellow coloration and the additional cost that itgenerates may become unacceptable for certain applications. Theultraviolet absorption due to the high titanium contents may also beunacceptable when the fibres are intended for reinforcing polymers thatare crosslinked by means of UV radiation. For these various reasons, thetitanium oxide content of the glasses according to the invention is lessthan 1% and preferably is equal to 0.9% or lower, and even 0.8%. Tobenefit from the advantages afforded by the presence of titanium oxide,its content is preferably 0.5% or higher.

Boric anhydride B₂O₃ is added to the composition of the glassesaccording to the invention, in a content greater than 0.1%, so as tofacilitate the melting and forming of the glasses. Boron may in fact beintroduced in a moderate amount, and inexpensively, by theincorporation, as batch material, of glass strand waste containingboron, for example E-glass strand waste. Another inexpensive means ofintroducing small amounts of boron consists in using natural batchmaterials providing boron oxide and alkali metal oxides, such as, forexample, borax (chemical formula Na₂B₄O₇.5H₂O). Since such batchmaterials provide sodium, and, owing to the limitation of the totalalkali metal oxide content which is desired, the boron oxide content ofthe glasses according to the invention is strictly less than 1.8%.However, the inventors have demonstrated its deleterious role on theacid corrosion resistance properties and the high-temperature resistanceproperties. The B₂O₃ content is thus preferably less than 1.5%, and evenmore preferably less than 1.1%. However, it has been discovered that lowboron oxide contents, which are particularly beneficial for the meltingand forming of the glasses according to the invention, do not degradethe abovementioned properties very appreciably. A minimum content of0.5% of boron oxide is therefore preferred in the glasses according tothe invention. When the B₂O₃ content is greater than or equal to 0.5%and the TiO₂ content is less than 0.5%, it is desirable for the SiO₂content to be greater than 60.5% so as to retain the good acid corrosionresistance properties.

Zinc oxide (ZnO) is used to reduce the viscosity of the glassesaccording to the invention and to increase their acid corrosionresistance. However, owing to the high cost of this oxide, its contentis less than 0.4%, preferably less than 0.1%.

The manganese oxide content is less than 1% and preferably less than0.3%. Since this oxide is liable to give the glass a very intensiveviolet coloration, the MnO content is preferably maintained below 0.1%.

Fluorine may be added in a small amount in order to improve the meltingof the glass, or it may be present as an impurity. However, it has beendiscovered that small amounts of fluorine affect the temperatureresistance of the glasses according to the invention very markedly. Thefluorine content is therefore advantageously maintained below 0.5% andespecially below 0.1%.

Iron oxide is an unavoidable impurity in the glasses according to theinvention owing to its presence in several batch materials, and itscontent is generally less than 0.5%. Given that the coloration effectgenerally attributed to titanium is in fact due to electron transferbetween Fe²⁺ and Ti⁴⁺ ions, the iron content in the glasses according tothe invention is advantageously less than 0.3%, especially less than0.2%, thanks to a judicious choice of batch materials.

One or more other components (differing from those already considered,i.e. different from SiO₂, Al₂O₃, CaO, MgO, Na₂O, K₂O, Li₂O, B₂O₃, TiO₂,F, Fe₂O₃, ZnO, MnO) may also be present, generally as impurities, in thecomposition according to the invention, the total content of these othercomponents remaining less than 1%, preferably less than 0.5%, thecontent of each of these other components generally not exceeding 0.5%.

The glass strands according to the invention may be produced andemployed like E-glass strands. They are also less expensive and exhibitbetter temperature resistance, acid corrosion resistance and tensilestrength.

The glass strands according to the invention are obtained from glasseswith the composition described above using the following process: amultiplicity of molten glass streams emanating from a multiplicity oforifices dispersed over the base of one or more bushings are attenuatedinto the form of one or more webs of continuous filaments, and thenassembled into one or more strands that are collected on a movingsupport. This may be a rotating support when the strands are collectedin the form of bound packages, or a support that moves translationally,when the strands are chopped by a member that also serves to attenuatethem, or when the strands are sprayed by a member serving to attenuatethem in order to form a mat.

The strands obtained, optionally after other conversion operations, maythus be in various forms, namely continuous strands, chopped strands,braids, tapes, mats, networks, etc., these strands being composed offilaments with a diameter possibly ranging from 5 to 30 microns,approximately.

The molten glass feeding the bushings is obtained from batch materialsthat may be pure (for example coming from the chemical industry) but areoften natural, these batch materials sometimes containing impurities intrace amount and being mixed in appropriate proportions in order toobtain the desired composition, and then melted. The temperature of themolten glass (and therefore its viscosity) is conventionally set by theoperator so as to allow the glass to be fiberized, while in particularavoiding problems of devitrification, and so as to obtain the bestpossible quality of the glass strands. Before they are assembled in theform of strands, the filaments are generally coated with a sizingcomposition for protecting them from abrasion and facilitating theirsubsequent association with materials to be reinforced.

The composites obtained from the strands according to the inventioncomprise at least one organic material and/or at least one inorganicmaterial and glass strands, at least some of the strands being glassstrands according to the invention.

Optionally, the glass strands according to the invention may havealready been associated, for example during attenuation, with filamentsof organic material so as to obtain composite strands. By extension, theexpression “glass strands whose composition comprises . . . ” isunderstood to mean, according to the invention, “strands formed fromfilaments of glass whose composition comprises . . . ”, the glassfilaments being optionally combined with organic filaments before thefilaments are assembled as strands.

Owing to their good high-temperature resistance properties, the glassstrands according to the invention may also be used for furnishing motorvehicle exhaust systems. In this particular application, the glassstrands according to the invention give good acoustic insulationproperties, but they are also exposed to temperatures that may exceed850° C. or even 900° C.

The advantages afforded by the glass strands according to the inventionwill be more fully appreciated through the following examples, whichillustrate the present invention without however limiting it.

Table 1 gives five examples according to the invention, numbered 1 to 5,and three comparative examples, numbered C1 to C3. C1 is a standardE-glass composition and C2 is a composition deriving from PatentApplication WO 99/12858, while C3 is according to the teaching ofApplication WO 96/39362.

The composition of the glasses is expressed as percentages of oxides byweight.

To illustrate the advantages of the glass compositions according to theinvention, Table 1 presents four fundamental properties:

-   -   the temperature corresponding to a viscosity of 10^(2.5) poise,        denoted by T_(log 2.5) and expressed in degrees Celsius, close        to the temperature of the glass in the bushing;    -   the difference between the latter temperature and the liquidus        temperature (termed T_(liq)), which represents a forming margin        that has to be as high as possible;    -   the softening temperature or Littleton softening point,        corresponding to a viscosity of 10^(7.6) poise, denoted by        T_(log 7.6) and expressed in degrees Celsius, this value being        indicative of the temperature resistance of the fibres, these        two temperature values and their respective method of        measurement being well known to those skilled in the art; and    -   the value of the failure stress in three-point bending of        composites based on vinyl ester resin (sold by Dow Chemical        Company under the name Derakane 411-350) comprising a fibre        volume fraction of 50% after immersion in a hydrochloric acid        solution (HCl of 1N concentration) at room temperature for 100        hours. This stress is expressed in MPa and characterizes the        resistance of the fibres to acid corrosion.

TABLE 1 C1 C2 C3 1 2 3 4 5 SiO₂ 54.4 59.7 60.1 60.1 60.9 60.9 60.2 60.2Al₂O₃ 14.5 13.2 12.8 13.0 12.2 12.2 12.5 12.7 CaO 22.1 22.2 23.1 22.022.2 21.9 22.0 22.0 B₂O₃ 7.3 — — 0.7 1.0 1.5 1.0 0.5 Na₂O 0.5 0.9 0.30.4 0.4 0.4 0.4 0.4 MgO 0.25 2.4 3.3 3.1 2.6 2.4 2.4 3.0 TiO₂ 0.1 — — —— — 0.8 0.5 K₂O 0.35 0.4 0.2 0.4 0.4 0.4 0.4 0.4 F — 0.9 — — — — — —T_(log2.5) (° C.) 1285 1341 1350 1356 1359 1360 1358 1357 T_(log2.5) −T_(liq) 205 161 150 185 175 185 195 175 (° C.) T_(log7.6) (° C.) 836 881920 916 920 918 923 923 Failure 200 420 550 500 545 540 550 540 stress(MPa)

As indicated in Table 1, the fibres according to the invention are verysubstantially superior to the E-glass fibres (Comparative Example C1) interms of temperature resistance (the difference of about 100° C.) and ofacid corrosion resistance (an at least two to three times higher failurestress).

The fibres according to the invention have usage properties that arequite similar to those of Example C3, but have the advantage of havingimproved fiberizing conditions, since the forming margin is appreciablymore comfortable (at least 25° C. higher) and even approaches conditionsfor E-glass, thanks to the moderate addition of boric anhydride. Thefibres according to the invention are in all points superior to thefibres of Comparative Example C2.

Examples 1, 2 and 3 illustrate the influence of certain oxides on theacid corrosion resistance of the fibres. Example 2 for exampleillustrates, by comparison with Example 1, the beneficial role of SiO₂and the prejudicial role of Al₂O₃, whereas Example 3 shows, comparedwith Example 2, the deleterious influence of boron oxide.

Examples 4 and 5 contain titanium oxide TiO₂. Comparing Examples 4 and2, it is possible to demonstrate the beneficial role of this oxide onthe temperature resistance, but also on the acid corrosion resistance,since the latter is improved despite the higher Al₂O₃ content and thelower SiO₂ content in Example 4.

The temperature and acid corrosion resistance properties and thefiberizing properties of the glasses according to the invention aretherefore particularly well optimized.

1. Glass strand, characterized in that its composition comprises thefollowing constituents in the limits defined below, expressed aspercentages by weight: SiO₂ 59 to 63 Al₂O₃ 10 to 16 CaO 16 to 23 MgO 1to less than 3.2 Na₂O + K₂O + Li₂O 0 to 2 TiO₂ 0 to 1 B2O₃ 0.1 to lessthan 1.8 Li₂O 0 to 0.5 ZnO 0 to 0.5 MnO 0 to 1 F 0 to 0.5.


2. Glass strand according to claim 1, formed from a glass melt obtainedby melting a batch characterized in that the said batch includes borax.3. Glass strand according to claim 1, characterized in that the TiO₂content is greater than or equal to 0.5%.
 4. Glass strand according toclaim 1, characterized in that the B₂O₃ content is greater than or equalto 0.5%.
 5. Glass strand according to claim 4, characterized in that,when the TiO₂ content is less than or equal to 0.5%, the SiO₂ content isgreater than 60.5%.
 6. Glass strand according to claim 1, characterizedin that the MgO content is greater than or equal to 2.2%.
 7. Composite,consisting of glass strands and organic and/or inorganic material(s),characterized in at it comprises glass strands as defined in claims 1.8. Fitting for an exhaust system, characterized in that it comprisesfibres as defined in claim
 1. 9. Glass composition suitable forproducing glass reinforcement fibres, which comprises the followingconstituents in the limits defined below, expressed as percentages byweight: SiO₂ 59 to 63 Al₂O₃ 10 to 16 CaO 16 to 23 MgO 1 to less than 3.2Na₂O + K₂O + Li₂O 0 to 2 TiO₂ 0 to 1 B₂O₃ 0.1 to less than 1.8 Li₂O 0 to0.5 ZnO 0 to 0.5 MnO 0 to 1 MnO 0 to 1 F 0 to 0.5.


10. Process for manufacturing glass strands, comprising the steps ofattenuation into the form of one or more webs of continuous filamentsfrom a multiplicity of molten glass streams emanating from amultiplicity of orifices placed at the base of one or more bushings, andof assembling the said filaments into one or more strands that arecollected on a moving support, the molten glass feeding the bushingshaving a composition according to claim 9.